page_title: Montana
section_title: Climate
hierarchical_section_title: Montana / Geography / Climate
caption_attribution_description: English: The Big Drift is a seasonal snow accumulation that occurs along the Going-to-the-Sun Road in Glacier National Park. The snowdrift can accumulate over 30 meters/100 feet deep and is located immediately east of the Continental Divide.
context_page_description: Montana is a state in the Northwestern United States. Montana has several nicknames, although none are official, including "Big Sky Country" and "The Treasure State", and slogans that include "Land of the Shining Mountains" and more recently "The Last Best Place".
  Montana is the fourth-largest in area, the 8th least populous, and the third-least densely populated of the 50 U.S. states. The western half of Montana contains numerous mountain ranges. Smaller mountain ranges are found throughout the state. In all, 77 named ranges are part of the Rocky Mountains. The eastern half of Montana is characterized by western prairie terrain and badlands. Montana is bordered by Idaho to the west, Wyoming to the south, North Dakota and South Dakota to the east, and the Canadian provinces of British Columbia, Alberta, and Saskatchewan to the north.
  The economy is primarily based on agriculture, including ranching and cereal grain farming. Other significant economic resources include oil, gas, coal, hard rock mining, and lumber. The health care, service, and government sectors also are significant to the state's economy.
  The state's fastest-growing sector is tourism.
context_section_description: Montana is a large state with considerable variation in geography, topography and altitude, and the climate is, therefore, equally varied. The state spans from below the 45th parallel (the line equidistant between the equator and North Pole) to the 49th parallel, and elevations range from under 2,000 feet (610 m) to nearly 13,000 feet (4,000 m) above sea level. The western half is mountainous, interrupted by numerous large valleys. Eastern Montana comprises plains and badlands, broken by hills and isolated mountain ranges, and has a semiarid, continental climate (Köppen climate classification BSk). The Continental Divide has a considerable effect on the climate, as it restricts the flow of warmer air from the Pacific from moving east, and drier continental air from moving west. The area west of the divide has a modified northern Pacific Coast climate, with milder winters, cooler summers, less wind, and a longer growing season. Low clouds and fog often form in the valleys west of the divide in winter, but this is rarely seen in the east.
  Average daytime temperatures vary from 28 °F or −2.2 °C in January to 84.5 °F or 29.2 °C in July. The variation in geography leads to great variation in temperature. The highest observed summer temperature was 117 °F or 47.2 °C at Glendive on July 20, 1893, and Medicine Lake on July 5, 1937. Throughout the state, summer nights are generally cool and pleasant. Extreme hot weather is less common above 4,000 feet or 1,200 meters. Snowfall has been recorded in all months of the year in the more mountainous areas of central and western Montana, though it is rare in July and August.
  The coldest temperature on record for Montana is also the coldest temperature for the contiguous United States. On January 20, 1954, −70 °F or −56.7 °C was recorded at a gold mining camp near Rogers Pass. Temperatures vary greatly on cold nights, and Helena, 40 miles (64 km) to the southeast had a low of only −36 °F or −37.8 °C on the same date, and an all-time record low of −42 °F or −41.1 °C. Winter cold spells are usually the result of cold continental air coming south from Canada. The front is often well defined, causing a large temperature drop in a 24-hour period. Conversely, air flow from the southwest results in "chinooks". These steady 25–50 mph (40–80 km/h) (or more) winds can suddenly warm parts of Montana, especially areas just to the east of the mountains, where temperatures sometimes rise up to 50–60 °F (10.0–15.6 °C) for 10 days or longer.
  Loma is the site of the most extreme recorded temperature change in a 24-hour period in the United States. On January 15, 1972, a chinook wind blew in and the temperature rose from −54 to 49 °F (−47.8 to 9.4 °C).
  Average annual precipitation is 15 inches (380 mm), but great variations are seen. The mountain ranges block the moist Pacific air, holding moisture in the western valleys, and creating rain shadows to the east. Heron, in the west, receives the most precipitation, 34.70 inches (881 mm). On the eastern (leeward) side of a mountain range, the valleys are much drier; Lonepine averages 11.45 inches (291 mm), and Deer Lodge 11.00 inches (279 mm) of precipitation. The mountains can receive over 100 inches (2,500 mm), for example the Grinnell Glacier in Glacier National Park gets 105 inches (2,700 mm). An area southwest of Belfry averaged only 6.59 inches (167 mm) over a 16-year period. Most of the larger cities get 30 to 50 inches or 0.76 to 1.27 meters of snow each year. Mountain ranges can accumulate 300 inches or 7.62 meters of snow during a winter. Heavy snowstorms may occur from September through May, though most snow falls from November to March.
  The climate has become warmer in Montana and continues to do so. The glaciers in Glacier National Park have receded and are predicted to melt away completely in a few decades. Many Montana cities set heat records during July 2007, the hottest month ever recorded in Montana. Winters are warmer, too, and have fewer cold spells. Previously, these cold spells had killed off bark beetles, but these are now attacking the
caption: The Big Drift covering the Going-to-the-Sun Road in Glacier National Park, as photographed on March 23, 2006
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